Here is how Amazon Game Studios explains the game: "Earth is threatened by an alien species, the Ne'ahtu. Early in the 22nd century, the Ne'ahtu infected Earth's energy grid with a computer virus that disabled the planet's defenses. Before the Ne'ahtu could strike, computer prodigy Amy Ramanujan neutralized the alien computer virus and saved the planet. Now, the Ne'ahtu are back and Dr. Ramanujan is trying to prevent them from another all-out invasion of Earth. Switching between towers (to launch various missiles and grenades) and face-to-face combat (to attack with machine guns), the player's mission is to join Dr. Ramanujan and defend Earth from the Ne'ahtu.

In Sev Zero, players can jump between environments--start in tower defense mode to build out towers and assess the surroundings, and then beam down to shooter mode for face-to-face combat against the Ne'ahtu. Players can also bring friends and family into the action with the Sev Zero companion tablet app, Sev Zero: Air Support. With this multi-player, multi-screen experience, players help each other thwart the enemies--one player is in Air Support mode initiating air strikes from their tablet while the other player is in face-to-face combat mode."

The game will cost you $6.99 and you will need Amazon's $39.99 game controller to play.